Liquid fabric treatment compositions suitable for fabric softening and static control during the laundry process are well known in the art and widespread in commercial success. These liquid fabric treatment compositions typically contain quaternary ammonium cationic surfactants (commonly referred to as quats) that provide fabric-softening and anti-static benefit during the laundry rinse cycle. The quaternary fabric conditioning agents, often comprising long chain fatty alkyl groups, tend to be water-insoluble, making it difficult to produce a stable concentrated liquid product with anything more than about 10% quaternary actives. For many consumer and institutional cleaning products, it is desirable to market concentrated products in order to reduce shipping, warehousing and handling cost, to reduce plastic packaging waste in the environment, and to make product that is easier to pick up and use by the consumer. Although it is relatively simple to concentrate laundry detergents into stable highly active compositions, there are not many practical methods to prepare concentrated liquid fabric softener compositions with high levels of quaternary and still maintain both phase stability and control of the overall viscosity such that the product may be easily poured.
Many of the various solutions to the problem of preparing concentrated yet stable and pourable liquid fabric softener compositions have not been completely satisfactory. For example, electrolytes such as calcium chloride have been used to control viscosity, however addition of up to about 2000 ppm CaCl2 does nothing more than allow a few more percent active quaternary to be added to the formula. This is exemplified in U.S. Pat. No. 3,681,241 (Rudy at al.) wherein formulations comprising only up to about 12% active quaternary are possible. This is also exemplified in U.S. Pat. No. 4,772,404 (Fox et al.) where formulas having up to 15% quaternary blend (Varisoft 222LM and Adogen 442 in a critical ratio) are stabilized with triethanolammonium citrate and 0.09% calcium chloride. Another approach has been to combine fabric “softener” and fabric “substantive” agents. For example U.S. Pat. Nos. 4,155,855 (Goffinet, et al.), 4,157,307 (Jaeger et al.) and 4,855,072 (Trinh et al), describe combination of fabric softening and fabric substantive agents, wherein the fabric substantive agent is a quaternary imidazolinium salt. However, even though the compositions may contain as much as 25-50% of a blend of these two quaternary materials, only the softening agent (a conventional quaternary) confers the softening and antistatic benefit to the fabric.
Other methods to stabilize concentrated fabric softener compositions having high levels of quaternary actives utilize additional surfactants, solvents or polymers. For example, as described in U.S. Pat. No. 4,326,965 (Lips et al.), stable formulas with up to 40% active quaternary are possible when incorporating 4-25% polymer having MW greater than 400. U.S. Pat. No. 4,556,502 (Blackmore et al.) describes concentrated fabric softener formulations with up to 40% active quaternary if stabilized with greater than 0.5% amphoteric surfactants and 5-30% alkanol solvent. Lastly, U.S. Pat. No. 4,233,164 (Davis) describes stabilization of 2-11% quaternary active formulations through the use of 1-5% nonionic surfactant.
Accordingly, fabric softeners having high levels of common quaternary ammonium cationic surfactants that remain creamy, phase-stable and pourable, without the addition of costly, extraneous and inactive ingredients are highly desirable.